1. Field of the Invention
The invention concerns a communication system for organizations and in particular for businesses whose communications are assured via a private telecommunication network with international coverage and via at least one other telecommunication network, these networks enabling calls to be set up between users via terminals at least some of which are mobile radio terminals designed to communicate in a digital cellular radio network of the DECT or the GSM global mobile communication system type.
2. Description of the Prior Art
Any call involving a mobile radio terminal is set up via a base station of the cellular network within range of which the mobile radio terminal is located during at least part of the call. The base station is connected to a routing subsystem, usually of the fixed telecommunication network type, via which the call between the mobile radio terminal and another called or calling terminal is routed. The base station is generally part of a radio subsystem that assures and manages all radio transmission to and from mobile terminals and that generally includes a plurality of base stations geographically distributed over the coverage territory offered to mobile radio terminals.
In many cases the routing subsystem uses pre-existing parts of fixed networks and in particular of switched telecommunication networks, in which case it has an at least partially meshed structure and generally includes a plurality of interconnection nodes. There is then usually a choice of several possible paths for connecting a calling party and a called party, the choice being made by the manager(s) of the network(s) that can be used for the same call. Call costs and conditions can vary significantly with the path selected when there are several co-existing choices.
This fact can be exploited by large organizations and in particular the large businesses referred to above, at least some of whose calls can be assured either via their own private network or via at least one other public and/or shared network. The choice can be made by the management structure of the private network on the basis of possibilities and requirements.
In the case of calls involving a mobile radio terminal this possibility is of benefit, in particular in terms of the cost to the organization.
Although a mobile radio terminal may give users the initiative for calls when they are within radio range of a base station of a digital cellular radio network with which they are compatible, users are not usually allowed to pre-empt a communication path to a terminal with which they wish to communicate from the base station to be used as an intermediary.